The present invention relates to a process for the iodination of perfluoropolyether acylhalides having the formula:
XCOxe2x80x94CF2O[(CF2O)n(CF2CF2O)m]pCF2xe2x80x94Qxe2x80x83xe2x80x83(II)
wherein X, Q and the indexes have the values defined hereunder to obtain perfluoropolyethers having iodinated xe2x80x94CF2I end groups with high yields.
The iodinated perfluoropolyethers are usable as oleohydro-repellent compounds, or as components for preparing fluororesins, fluoroelastomers; or used as precursor of fluorinated surfactants.
Methods to iodinate perfluoropolyether acylhalides are known in the prior art, but having repeating units different from those of formula (II).
The iodination is for example carried out by reacting an acylfluoride with iodine in the presence of a perhalogenated solvent and of an alkaline or alkaline-earth metal carbonate, as described for example in EP 348,948. As an example of perhalogenated solvent hexachloro-1-3-butadiene is mentioned. The drawback of this process is that hexachloro-1-3-butadiene is not a solvent usable from an industrial point of view since it is an irritating compound.
Another process for preparing iododerivatives of perfluoropolyethers having a structure different from that shown in (II) is reported in EP 520,821 which describes the reaction of an acylfluoride with a metal iodide, wherein the metal is for example Li, Na, Mg, Ca, Al, to form perfluoropolyethers having xe2x80x94COI end groups. According to this patent the reaction takes place at temperatures between 0xc2x0 C. and 100xc2x0 C., and in a subsequent step the irradiation of the obtained compound is carried out by UV rays at room temperature, obtaining the perfluoropolyether with iodinated end groups. The drawback of said process is to comprise two distinct steps and to use a UV ray source, which as well known requires rather complex plants to be industrially operated.
The need was felt to have available a process for preparing perfluoropolyethers having one or both the end groups with an iodine atom starting from linear perfluoropolyether monoacyl- or diacyl-halides, having structure (II), which allowed to obtain products having high yields, without substantially modifying the number average molecular weight Mn, of the starting product of structure (II), said average molecular weight being considered without the two xe2x80x94COX end groups.
An object of the present invention is a process for preparing perfluoropolyether iodides, by reaction with LiI of monoacyl- or diacyl-halides of perfluoropolyethers, having a number average molecular weight from 200 to 3,000, preferably from 500 to 3,000, still more preferably from 1,000 to 3,000, and having the following structure:
XCOxe2x80x94CF2O[(CF2O)n(CF2CF2O)m]pCF2xe2x80x94Qxe2x80x83xe2x80x83(II)
wherein:
m/n=0.5-10; p=0-20;
X=Cl, F;
Q=H, CF3, X as above defined or COXxe2x80x2, wherein Xxe2x80x2 is Cl, F with the proviso that Xxe2x80x2=X;
said process being characterized in that the iodination reaction is carried out in a reactor, at a temperature from 180xc2x0 C. to 260xc2x0 C., preferably from 185xc2x0 C. to 220xc2x0 C.
The process of the present invention can operate both in the presence and in absence of solvents.
As solvents, those which solubilize the perfluoropolyethers of formula (II) are used. Acetonitrile, perfluorooctane, etc. can for example be mentioned.
Preferably in the process of the invention in formula (II) X=Xxe2x80x2=F.
The ratio by moles between LiI and xe2x80x94OCF2COX end groups ranges from 1.1 to 2.
The reaction time is that necessary to reach the total conversion of the perfluoropolyether halide in the corresponding iodide at the selected reaction temperature. Generally the reaction is considered over when in the reactor a pressure value is reached which remains constant at the selected reaction temperature. Generally reaction times of 4-6 hours are sufficient to end the reaction.
In the sealed reactor used in the process according to the present invention, before starting the reaction, the gases are removed by reducing the internal pressure.
The iodinated perfluoropolyether compounds obtained with the process of the invention have the following formula:
Ixe2x80x94CF2O[(CF2O)n(CF2CF2O)m]pCF2xe2x80x94Txe2x80x83xe2x80x83(I)
wherein T=I, F, CF3, H, Cl; m/n=0.5-10, p=0-20 and having average number molecular weight from 200 to 3,000.
The results of the present invention are particularly surprising and unexpected since in the prior art the preparation of iodinated compounds of perfluoropolyethers having structure (I) has never been described. Indeed in the starting compounds of structure (II), xe2x80x94OCF2Oxe2x80x94units (Cl unit) in position xcex2 with respect to the xe2x80x94COX end group are present in the structure. When the structure of the fluorinated acylhalide compound comprises the aforesaid groups, contemporaneously with the iodination the secondary reaction of xcex2-scission takes place. This causes the decrease of Cl units in the perfluoropolyether structure, with formation of carbonyl fluoride COF2. Therefore the xcex2-scission reaction causes a mass loss of the final product. It has been found by the Applicant that the effect of this secondary reaction is particularly evident when an iodinating agent different from LiI is used.
By operating with the process of the invention it has been unexpectedly found that the xcex2-scission reaction can be remarkably reduced or substantially eliminated.
The following Examples illustrate the invention but they do not limit the scope thereof.